Canada finds another new flu strain in farm workers

Jul 8, 2009 (CIDRAP News) – Public health officials in Canada yesterday announced that they have detected a new influenza strain—one that contains human seasonal flu and a swine flu virus—in two workers on a Saskatchewan hog farm.

The workers had mild illness and have recovered, and authorities are investigating a third suspected case, the Public Health Agency of Canada said in statement yesterday.

Canada's health minister Leona Ablukkaq said federal officials are working with Saskatchewan to learn more about the new virus. "Preliminary results indicate the risk to public health is low and that Canadians who have been vaccinated against the regular, seasonal flu should have some immunity to this new flu strain," she said in the statement.

Dr Greg Douglas, Saskatchewan's chief veterinary officer, told Reuters today that the new virus contains genes from the seasonal human H1N1 flu strain and a triple reassortant H3N2 strain that is common in swine populations.

Initial testing on the pigs indicates they were infected with swine influenza A, common in swine herds, but not the new human strain found in the workers, the Public Health Agency said. Further surveillance will be conducted on Saskatchewan's hog industry workers, and the Canadian Food Inspection Agency is providing the province with guidance on swine herd surveillance.

Saskatchewan's health agency said in a statement yesterday that additional responses include reinforcing biosecurity measures at the affected farm and vaccinating the hog farm's workers.

It added that in most cases, viruses such as the one found in the hog farm workers are not transmitted easily between humans. "To date, there is no evidence that this strain has transmitted between humans," the agency said.

Douglas, the province's chief veterinary officer, said in the statement, "It is important to remember that only healthy hogs go to slaughter and that pork is safe to eat. Influenza is not transmitted by eating pork products."

Canada said it has notified the World Health Organization (WHO) about the new virus, as required under international health regulations.

Dr Carolyn Bridges, associate director of epidemiologic science in the US Center for Disease Control and Prevention's (CDC's) influenza division, told CIDRAP News that the reassortment event in Canada isn't surprising. "We know that humans pass influenza viruses to pigs on a regular basis," she said, adding that the human seasonal H3N2 influenza virus first entered North American swine herds in 1998 and that multiple reassortment events have been detected since then.

"This is just another demonstration of how dynamic these viruses are," Bridges said.

The virus detected in Canadian hog farm workers is not a pandemic flu threat because it contains external human virus proteins—the part the immune system recognizes, she said. "That's what matters most, and the flu vaccine provides good coverage. A large proportion of the population has some preexisting immunity." Sustained transmission of the new virus among humans is unlikely, she added.

However, the events highlight the need for ongoing surveillance in pig populations to monitor for changes, Bridges said.